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Footings against retaining wall
My garden is approximately 1 metre higher than my neighbours, with an old but solid retaining wall. I want to partly replace the fence which sits on my side of the retaining wall with a new wall - about 4 metres long.
The new wall will be about 2 metres high, and as it is in a very exposed position I have decided to build it 1 & 1/2 bricks thick ie 325mm. I want to get the new wall built as close as possible to the retaining wall, so I don't take up too much of my garden. But I do not want to damage the integrity of the existing wall (and I also don’t know who owns it) so I don’t want to build onto it in any way.
The difficulty I foresee is that the technical advice I have read suggests that such a wall should sit in the centre of 775mm wide footing - meaning that there will be a gap of at least 225 mm between the retaining wall and the new wall.
So the question is, how do I construct foundations that allow the new wall to be built against the retaining wall. I have seen some information about constructing an eccentric footing (but not enough to tell me how it is done) and also wondered about using some lightweight screw piles, with a narrower concrete pad on top. I will be getting a professional to do the work, but I’d like to understand what the options are. Any suggestions would be very welcome.
Sorry this is a bit long, but I would welcome views.
Thanks for the two answers - I appreciate the replies. I have had a rethink and now going for a totally different solution. Relatively lightweight Corten steel panels 320 kgs in total - 4 metres long and 2 metres high. Mounted on hardwood timber, with cross timbers taking the weight away from the retaining wall and 2 metres back from the wall.
2 Answers from MyBuilder Bricklayers
Hello, thank you for your question.
Your retaining wall should have a concrete foundation that is 600 mm wide by 300 mm deep. To build your new wall at a 20mm distance from the retaining wall you would have build a foundation extension (exactly near the foundation of the existing retaining wall) that is 600 mm wide by 450mm deep and match the two foundations by drilling into the foundation of the existing retaining wall and installing iron rods.
Your new wall would be 338mm thick and, (if the retaining wall is already 1m) a total of 3 m high in order to have a 2 m tall wall above the ground of your garden.
You would have to use class B engineer bricks for the first 13 courses of the wall (below the ground). The first 13 courses of your new wall will be considered to be part of a retaining wall.
Good luck with your project!
Answered 28th Sep 2020
300 mm of concrete for a two metre high wall ???????? the above answer ,I'm no structual engineer but a 600 mm wide 300 mm deep foundtain is not enough ,you mention that the wall will be a exposed position as well ,As the proposed wall is to be 338 mm wide i suggest a foundation to be 850mm wide and at least 900mm deep with 600mm mass filled of concrete ,hope this helps
Answered 25th Nov 2020
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